Hello there as well,
I've the same issue and I investigate the problem. The reason why it does not work is, that the racoon (IKE Daemon) does not accept connections on port 4500 (IKE for NAT-T) if the source port is random generated.
Since Mavericks and IOS7 the source port from the client is no longer 4500, this lead to this problem (except you have a old VPN connection already setup bevor you update to IOS7 on your Phone).
If you are in the same network like your server, the IKE NAT-T is not used. In this case the regular port 500 (IKE) is used, and this works as expected. At the moment we have to wait if the problem is fixed by Apple.
There are two possibilities, they can adjust the clients or the server configuration. However if you want to use VPN with OS X native methods, use PPTP. This is not affected but of course it provides no Layer 2 Tunneling.
Regards,
Daniel